Writer, ethology enthusiast, axolotl herder. Might possibly just be a Lasiurus cinereus that types with its thumbs.

COOL COSTUME IDEAS STRAIGHT FROM NATURE

Stuck on what costume to wear for this Halloween? Perhaps you should look to nature for some suggestions! Here are a few classics:

  • Placing sand, kelp, and stinging anemones all over your body
  • Covering yourself with feces and/or the corpses of your enemies
  • Urinating in mud and then bathing in it for an especially masculine look
  • Removing all your clothes and sticking a blade of grass in your ear

Truly, this is the best time of the year.

In the spirit of the season I thought I’d write a bit about animals that like to make costumes for themselves. In a strictly scientific sense, this is called “decorating behavior” and spans from full-body coverings to the most tastefully sparse jewelry. As for why animals decorate, the reasons vary. For example, the juveniles of one species are known to use it to signal the adults to give them sugar-rich substances. (I am referring, of course, to Trick-or-Treating.)

Before we delve deeper into what causes decorating behavior, though, let’s first make sure we understand what decorating behavior isn’t. With the exception of feces, excretions that come from the animal itself aren’t considered decorative. For example, when you brush your hair, it draws oil secretions from your scalp down the follicles- but you wouldn’t think of that as putting something in your hair, would you? Many animals ooze stuff that they rub on their bodies, but for it to count as decoration it must come from the external environment. Feces are an exception because they pretty much become part of the environment as soon as they make their way out of the body.

So, the first part of our decoration definition states that decorations must be something picked up from the environment. But not everything an animal picks up is a decoration. Food items aren’t, obviously. And neither are tools. For something to be considered decoration, an animal must place it on its body and retain it there. No eating, no lock-picking or anything like that. Nuts in a hamster’s cheek pouches do not count as decorations.

Have a good idea of what we’re talking about now? Ok, so let’s look at the many reasons why animals decorate themselves. The most popular and well-studied one is one you’ve already thought of- defense.

But defense against what? Your mind likely immediately jumps to ‘predators,’ but predators are honestly only one of many, many ways to die. I mean, humans don’t have predators, yet roughly 500,000 people managed to do themselves in by tripping over furniture in 2013. The environment is truly deadly.

Sea urchins cannot trip, given that they have no legs, but they do suffer environmental damage when currents smack them around and tangle seaweed up in their poky bits. Many urchins will cover themselves in little rocks in order to shield themselves from these hazards, which is amazing because I bet you never considered the fact that an animal composed nearly entirely of sharp points would need more defense.

This sea urchin has made a charming outfit out of seashells. (Photo by Brocken Inaglory. CC by SA 3.0)

This sea urchin has made a charming outfit out of seashells. (Photo by Brocken Inaglory. CC by SA 3.0)

The rocks also act like a very thick layer of sunscreen, protecting the urchin from UV damage. Keep that in mind as a feasible alternative the next time you forget your Coppertone at the beach.

Parasites are another non-predator hazard that many critters face; this is a common explanation for why so many animals roll around in mud. Yet you must also consider the danger of parasitoids, which are like parasites except they kill you in the end and burst out of your gut alien-style. Obviously this is something most animals are interested in avoiding, particularly the larvae of leaf beetles, who are aggressively attacked by wasps looking for a warm gooey place to lay their eggs. The larvae’s avenue of defense is to gather up bits of its shed skin and feces and weave them into a little umbrella using, I kid you not, a part of their anatomy called an ‘anal turret.’ They stick the shield onto another part of their anatomy with the equally charming name ‘anal fork.’

The poop umbrella also shields against weather hazards, and some species actually swing it around to deter predators. Amazing. (Photo by Manfred Kunz. CC BY-SA 3.0)

The poop umbrella also shields against weather hazards, and some species actually swing it around to deter predators. Amazing. (Photo by Manfred Kunz. CC BY-SA 3.0)

Now that you’ve digested that bit of information, let’s go into costumes that are strictly antipredator.

The most famous decorating animal is probably the aptly-named decorator crab. Though calling it the decorator crab is a bit of a misnomer, as many species of crab within the superfamily Majoidea (the spider crabs and relatives) decorate themselves, and the trait is not monophyletic. Apparently, the behavior was profitable enough to have evolved separately in multiple lineages. In any case, watching them decorate themselves is fascinating and adorable.

Without decorations, there is nothing particularly remarkable about the looks of a decorator crab species, aside from their being somewhat…. fuzzy. Like all crabs, their bodies are covered by a hard carapace (exoskeleton), but on this carapace they have millions of tiny, hooked setae that act like velcro.

Screen Shot 2015-10-31 at 12.08.04 PMBut it is highly unlikely that you will ever see a decorator crab that isn’t costumed. To them, nudity is more than embarrassing, it’s deadly. Multiple studies that all involved disrobing a poor crab have confirmed that they are much more likely to get picked off if in the buff.

Here is a naked spider crab. Let's, uh, cover that up. (Photo by Hans Hillewaert. CC by SA 4.0)

Here is a naked spider crab. Let’s, uh, cover that up. (Photo by Hans Hillewaert. CC by SA 4.0)

As to exactly how the crabs’ clothes work as a defense, that really depends on what it wears. Crabs that swathe themselves in sand, small rocks, and bits of kelp are usually going for basic camouflage. But many species also pick up other living animals- that is, sponges, bryozoans, algaes, and anemones- are usually trying to co-opt some chemical defense. All of these creatures can secrete noxious substances, and in the case of the anemone, deliver painful stings. You might think that these sessile organisms wouldn’t be very happy to be picked up and moved around, but it seems the benefits go both ways. The crab gets a potent predator deterrent, while the anemone, by virtue of being transported, is able to feed on diverse food items and gets better water flow through its tentacles, which helps with respiration.

I promise you, there is a crab under there. (Image from divegallery.)

I promise you, there is a crab under there. (Image from divegallery.)

Aside from all that, the decorator crabs get an additional defense boost simply by appearing larger. Many of their predators can’t swallow prey over a certain size limit.

Camouflaging with live animals is fairly unusual outside of the seafloor, however, since most terrestrial animals tend to move around too much to be considered decorations. On the other hand, as many taxidermists know, corpses and castoffs make a fine addition to any collection. The larvae of several species of assassin bugs weave ‘backpacks’ out of the actual dead bodies of their victims- ants, in most cases. After paralyzing the hapless critters and sucking out their internal fluids, the assassin bug bundles up the ant’s remaining exoskeleton in sticky thread it secretes from its abdomen and sticks it there.

This is an effective antipredator defense, as shown in at least one study, because most predators don’t like messing with ants- they bite, sting, and have a nasty habit of ganging up on you and ripping you into bite-sized pieces. Seeing an amorphous cloud of ants trundling around is apt to make any spider run far in the opposite direction. If they do manage to strike up the courage to attack, they’re likely to grab onto a faceful of dessicated ants while the bug itself continues merrily on its murdery way.

(Photo by Getty Images.)

I can’t forget my backpack if I’m going to assassin bug school! (Photo by Getty Images.)

Invertebrates are not the only creatures to change their looks via the environment. Some bird species, like the rock ptarmigan, disguise their feathers with mud in order to blend in when the winter snow melts. Curiously, only males display this behavior, which suggests that bright white plumage is attractive to the ladies (who molt into darker colors as soon as the season turns). In fact, males that dirtied themselves usually did so immediately after their mate laid eggs; aka, ‘now that she’s pregnant I no longer have to put effort into looking good!’ Nice one, guys.

Left: Clean ptarmigan. Right: A dirty, dirty bird.

Left: Clean ptarmigan. Right: A dirty, dirty bird.

Pigs are another group of animals well-known for getting dirty, or wallowing, as it’s called. This is not to hide, however, but for the dual purpose of suffocating parasites and cooling off via evaporation. Wild boars also use mud for another surprising reason: to look sexy. Males do most of their wallowing in autumn, not a particularly hot or parasite-ridden season- but one that coincides with the mating rut. As to why wallowing coincides with sexytimes, the scientific jury’s still out. But they aren’t the only ungulate (hoofed animal) to do this. The bucks of many deer species have a lovely habit of urinating on the ground and then wallowing in it, coating themselves with manly-stinking mud. Sometimes they even forego the mud and put their heads down to urinate directly on their own faces. Aren’t deer majestic.

Ungulates in general are just obsessed with pee. (Photo from IndiaWilds.)

Ungulates in general are just obsessed with pee. (Photo from IndiaWilds.)

Bearded vultures (which also go by the name lammergeier) also have a habit of rolling in mud, but it isn’t to disguise themselves, or to get rid of parasites, or even to attract mates. Though many have seen and admired the elegant look of the bearded vulture, with its pinkish-to-rusty chest plumage, few realize that this lovely color is actually not naturally occurring: bearded vultures kept in strict captivity actually have white chests and heads. Wild vultures attain their looks by bathing in iron-enriched mud and soil. Higher-ranking birds within the vulture hierarchy tend to have darker red feathers. This has lead some researchers to believe that the mud is a status symbol like human makeup, indicating that the bird has the leisure of seeking out this specific mud and rolling in it for long periods of time. In fact, they can spend over an hour staining themselves, and prefer to do so without being watched.

Variations in vultures.

Variations in vultures.

You can’t strictly call bearded vulture mud-staining a cultural thing, of course, because even birds raised by humans in captivity will perform the behavior: this means it’s innate, and it has a good evolutionary backing behind it. But animals who dress themselves up purely for its own sake do exist- animals besides humans, I mean. A recent paper on some of our closest relatives found that arbitrary self-decorating ‘fads’ can be passed around in chimpanzee. The fad in question was sticking a piece of grass in their ear.

(Photo by Smithsonian.)

(Photo by Smithsonian.)

This fashion statement was started by a chimpanzee named Julie for mysterious reasons- maybe she had an itchy ear?- but was quickly picked up by other members of the group. And again: there’s no evidence that having a blade of grass sticking out of your ear confers any actual benefit! Other local groups of chimps didn’t do it. It was purely cultural.

Costuming without a direct defensive or sexual benefit is, of course, pretty rare in the animal kingdom. This is because there are very specific costs to dressing up. The biggest one, of course, is carrying around that added weight. Hermit crabs, for example, can move a whole lot faster if they aren’t carrying a shell (but nobody wants that, because they are actually gross and hideous creatures without them).

PUT IT BACK! PUT IT BACK!!

PUT IT BACK! PUT IT BACK!!

Likewise, many costumes take a lot of energy just to construct. Caddisfly larvae build very elaborate and time-consuming butt cases out of sand or twigs or whatever detritus is in their environment. If you are an asshole like certain scientists are, you can remove the case and watch them struggle to build the whole thing all over again. Larvae that have to build cases several times end up actually being smaller as adults because of all the effort they have to expend.

Shh.... it's sleeping now.

Shh…. it’s sleeping now.

So that’s what animals wear! Hope this gave you a few costume ideas to scare the kids with!

References

Bacher, S. and Luder, S. (2005), Picky predators and the function of the faecal shield of a cassidine larva. Functional Ecology, 19: 263–272. doi:10.1111/j.1365-2435.2005.00954.x

Delhey, K., Peters, A., & Kempenaers, B. (2007). Cosmetic coloration in birds: occurrence, function, and evolution. the american naturalist, 169(S1), S145-S158.

Fernández-Llario, P. (2005). The sexual function of wallowing in male wild boar (Sus scrofa). Journal of Ethology, 23(1), 9-14.

HERREID, C. F., & FULL, R. J. (1986). Energetics of hermit crabs during locomotion: the cost of carrying a shell. Journal of Experimental Biology, 120(1), 297-308.

Hultgren, K., & Stachowicz, J. J. (2011). Camouflage in decorator crabs: integrating ecological, behavioural and evolutionary approaches. Animal Camouflage, 214-229.

Jackson, R. R., & Pollard, S. D. (2007). Bugs with backpacks deter vision‐guided predation by jumping spiders. Journal of Zoology, 273(4), 358-363.

Liu, Z., Ding, J., Song, Y., Zeng, Z., & Zhang, Q. (2007). Wallowing behavior of Hainan Eld’s deer Cervus eldi hainanus male during the rut and its function in reproduction.

Montgomerie, R., Lyon, B., & Holder, K. (2001). Dirty ptarmigan: behavioral modification of conspicuous male plumage. Behavioral Ecology, 12(4), 429-438.

Mondy, N., Rey, B., & Voituron, Y. (2012). The proximal costs of case construction in caddisflies: antioxidant and life history responses. The Journal of experimental biology, 215(19), 3453-3458.

Negro, J. J., Margalida, A., Hiraldo, F., & Heredia, R. (1999). The function of the cosmetic coloration of bearded vultures: when art imitates life. Animal Behaviour, 58(5), F14-F17.

Ruxton, G. D., & Stevens, M. (2015). The evolutionary ecology of decorating behaviour. Biology letters, 11(6), 20150325.

Van Leeuwen, E. J., Cronin, K. A., & Haun, D. B. (2014). A group-specific arbitrary tradition in chimpanzees (Pan troglodytes). Animal cognition, 17(6), 1421-1425.

Beyond the Bars: Ethical Enclosures for Captive Animals (Part Two)

How Can We Tell When Animal Welfare is Good?

In the previous article, I gave a drawn-out description of some of the theory and history of modern animal enclosure design. But I haven’t much discussed the thing itself. I am, of course, going to– but first we have to lay down a few ground rules.

Remember when I was describing the difficulty I had designing my axolotl tank? Namely, the part about what I thought was aesthetically pleasing being different than what they actually found comfortable to live in. Similarly, it is hard to gauge the quality of an animal’s captive environment by looks alone. In modern husbandry, an animal’s welfare is determined on the basis of three main things, which are often interconnected:

Physical health: the most basic welfare requirement, and the most self-explanatory. Animals should be neither emaciated nor overweight and should not be showing signs of illness or injury. The early “sterile” zoos attempted to achieve this.

Presence of abnormal behaviors: this refers to behaviors such as stereotypies, self-injury, anhedonia, cognitive bias, et cetera, as well as exaggerated negative forms of normal behaviors such as overgrooming. The introduction of enrichment in zoos after the 60s served as a way to try to reduce or eliminate these types of behaviors.

Presence of species-typical behaviors: in other words, the animal performs behaviors that it might have if it lived in the wild. A monkey climbs, a cheetah scent-marks, a bird preens. The presentation of positive behaviors, rather than just the reduction of negative ones, is a relatively new concept to animal welfare, but one that is being implemented in many zoos, labs, and even farms around the world.

Now that I’ve brought up wild behaviors, though, I’d like to emphatically say that the goal of animal enclosure design is not to mimic wild conditions. Firstly, this is impossible even for the best captive situations. Secondly, what ideal wild conditions even are is not something easily defined. Consider, again, the wild axolotl: I am certainly not trying to mimic their polluted, drained wild habitat in my tanks. I am also not introducing their natural predators, parasites, competitors, and et cetera, even though that, too, would be more appropriately wild. The lives of wild and captive animals are very different- arguably, one is not objectively better than the other. Many wild animals have absolutely miserable- and short- lives.

Not, mind you, that many captive animals don’t suffer similarly abysmal fates. It’s simply that the stresses placed on wild and captive animals are very different. The largest of these differences is that most of the stresses placed on wild animals occur in temporary bursts followed by a period of relaxation. For example, a lioness goes hungry for several days, causing her great stress, but then makes a kill and is satiated for a good 48 hours. The impala that the lioness chased, on the other hand, are temporarily highly stressed at her pursuit over the course of those days, but have the opportunity to come down from that anxiety each time she feeds or gives up the hunt.

Neither predator anxiety or hunger should (theoretically) be a major source of stress for a captive animal. Instead of brief bursts of intense stress, captive animals suffer from low, constant levels of chronic stress. For example, the temperature in a reptile enclosure may constantly be just a few degrees colder than the reptile’s ideal climate range. This does not rapidly kill the animal as starvation or predation would, but it does begin to contribute to a gradual decline in health as the reptile’s body struggles, day in and day out, to cope.

One of the biggest concerns in captive animal welfare, then, is actually nearly invisible to us- this is why, again, I frown on short-term visual assessments as a good means of assessing welfare. Chronic stress is hard to measure accurately, especially in non-mammals whose needs and body language are less familiar to us. This is another reason why it is good to look for the presence of positive (i.e., species-typical) behaviors rather than just negative (i.e., abnormal) behaviors when assessing welfare. Animals under constant low levels of stress will often put their energy into vigilance or hiding behaviors- appearing as though they are not doing anything for long stretches of time.

Of course, the caveat to all this is that you need to have some understanding of what constitutes a suite of normal, species-typical behaviors for the animal in question, and in many cases this is difficult to impossible to obtain. In some cases, we are lucky enough to have extensive observations of wild animal behavior. For example: captive lions that spend eighteen to twenty hours each day sleeping or lying down might seem bored or too depressed to do anything else, but this ‘laziness’ is actually species-typical behavior for wild lions (who spend, on average, only three hours each day up on their feet). So this long-term lounging behavior is actually a positive sign for their welfare.

However, more often than not, we don’t have the luxury of these wild accounts, especially for many animals which are extremely difficult to observe in the wild, or simply haven’t warranted enough long-term study from the scientific community. This includes many species of birds, reptiles, fish, and amphibians. Those trying to care for these animals in captivity are then left with guesswork as to what their normal behavioral suite looks like, based on, say, what they might know about the behavior of closely-related animals, or those in similar niches. It is not a perfect solution by any means.

Pet owners, I feel, are some of the worst offenders as far as misunderstanding the wild behavioral suites of their animals go. In many cases they don’t even know the country of origin of their exotic fish or bird, much less its natural lifestyle. You should not buy any animal, ever, without knowing where it came from and what it does to make a living.

With all that said, the best animal enclosures will work to provide opportunities for species-typical behavior while minimizing chronic stressors. Sometimes, surprisingly enough, this can mean substituting temporary stressors instead! One example of this would be veterinary examinations and treatments- usually terribly stressful for the animal at the time, but overall good for preventing injury or disease from causing chronic stress. Think about this the next time you balk at going to the doctor or dentist.

Let’s begin a more detailed discussion on positive enclosure design with a very controversial element: available space.

Space

 

Space requirements for captive animals is a tricky subject. It is generally easily visible to observers and is often the first thing to be criticized about enclosures by visitors to zoos and other places. But most of these visual assessments are based on the amount of space a similarly-sized human would feel comfortable in, not the actual animal. So how can we assess how much space an animal needs to be free from anxiety and frustration?

At the most basic level, the minimum amount of space an animal needs should allow it to move unrestricted. The animal should be able to stand up, lie down, and turn around unhindered. This minimum is acceptable for very short-term housing such as veterinary cages, in which case limited space is important to prevent the animal from straining itself, as well as providing easy access to the animal so that it can be treated. In some cases, such as when the animals are being transported or treated for serious maladies, even more restrictive housing is acceptable, but again, this should be extremely-short term.

There is some controversy even in this most basic space requirement when it comes to large snakes. Most pet snakes and many zoo snakes are kept in enclosures that are too small to allow them to stretch to their full length. The most common explanation I've heard given for this is that the snakes are made more anxious by excess open space, and don't ever really need to stretch out fully. Indeed, this mindset was so pervasive that I believed it myself for a while. However, research suggests that this explanation serves the snake owner more than the snake itself. To start with, snakes have a single, elongated lung that can take up as much as half their body length which must have room to expand in order for the snake to breathe properly. Also, many wild snakes completely straighten their bodies out in order to resolve digestive issues. Captive snakes in enclosures that are shorter than their total body length are unable to perform this behavior. (Photo from Warwick et al., 2013.)

There is some controversy even in this most basic space requirement when it comes to large snakes. Most pet snakes and many zoo snakes are kept in enclosures that are too small to allow them to stretch to their full length. The most common explanation I’ve heard given for this is that the snakes are made more anxious by excess open space, and don’t ever really need to stretch out fully. Indeed, this mindset was so pervasive that I believed it myself for a while. However, research suggests that this explanation serves the snake owner more than the snake itself. To start with, snakes have a single, elongated lung that can take up as much as half their body length which must have room to expand in order for the snake to breathe properly. Also, many wild snakes completely straighten their bodies out in order to resolve digestive issues. Captive snakes in enclosures that are shorter than their total body length are unable to perform this behavior. (Photo from Warwick et al., 2013.)

Another form of short-term housing is a crate or kennel area that is blocked off from the main enclosure (which could be a yard or even your house). Again, this should be a temporary holding area, used for feeding, sleeping, access to the animal, or simply keeping the animal contained while the rest of the enclosure is cleaned. Some animal species may find crates or stalls comfortable and secure spaces to sleep in so long as they are given access to the larger enclosure for the bulk of their active hours.

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Many owners practice “crate training” with their dogs in order to secure them during periods of alone time or travel. While this is often successful, there are some caveats to this method. If crating is used as a punishment, or the dog is kept confined while vocalizing or attempting to escape, being crated will become a negative, stressful experience. Likewise, a dog should not be kept crated for more than three active hours (i.e., hours the dog is not spending asleep) each day. (Photo source, CC by SA 3.0)

Temporary confinement can also occasionally be a positive thing for an animal. Briefly restricting access to certain areas of the enclosure increases the amount of anticipation and excitement the animal feels before being allowed back in. Calves and baby goats, for example, spend much more time exploring and playing in a paddock if they are only given access to it for part of the day than if they are given free access to it all the time. Of course, if this restriction goes on too long, anticipation can give way to anxiety and frustration.

Beyond temporary areas, it’s hard to determine how much space an animal needs in its entire enclosure. The size of an animal’s body is not always a good indicator of how much space it needs. A monitor lizard, for example, is much larger than a rat, but spends much less time moving around due to a lower metabolism. So enclosure space isn’t necessarily a function of animal size alone but animal size as a function of animal activity level.

Yet even this is an oversimplification. Say you provide that highly active rat with a bedroom-sized floor space to run around in, with nothing to get in its way. The likely result will be that the rat will only utilize a tiny fraction of that space- namely, the corners and the parts of the floor directly adjacent to the walls. Why is this?

The answer is simple: rats are delicious, and running out into wide-open spaces is an excellent way for them to advertise that deliciousness to, say, a hawk. So that rat is going to avoid spaces where it feels exposed and vulnerable, effectively rendering most of the glorious open space you’ve provided it with useless.

So not only do you have to consider animal size and animal activity level, you also have to consider what activities the animal actually performs. In the case of the rat, you can convert all that useless space into usable space by providing it with a multitude of tunnels, shelters, and other hiding spaces throughout.

A much more suitable use of space for a rat enclosure than the open-field environment used for testing in the video above. Note how the use of vertical climbing areas increases the amount of space exponentially.

A much more suitable use of space for a rat enclosure than the open-field environment (used for testing in the video above). Note how the use of vertical climbing areas increases the amount of space available for use.

Similarly, for some animals, floor space matters little if at all. Perching bird species and arboreal climbers like climbing snakes and monkeys may feel very exposed touching what they perceive as the ground level. So again, that wide-open space you provide them will not work. These animals will need high vertical spaces rather than large floor spaces.

With this in mind, I’d go as far as to say that the amount of space you provide an animal matters much less than how you use that space. And this, again, is entirely based on what the particular species of animal needs.

"Cat shelves" are becoming more popular as a way for cat owners to allow their pets to utilize vertical space.

“Cat shelves” are steadily becoming more popular as a way for cat owners to allow their pets to utilize vertical space.

Animal species is actually not the only factor you need to take into account when considering how an animal will use a space. Male and female animals may be prone to using space in different ways, especially in regards to social and sexual behaviors. And juvenile animals are almost always more active than adult animals, so even though they’re smaller they may need larger spaces than adults of the same species.

When housing more than one animal together, the space needs to increased- but not as much as you might think. Social animals generally don’t spend their time at opposite ends of the enclosure, but rather close together so they can socialize. The caveat, of course, is that socially-housed animals need access to places where they can avoid or hide from their companions in case of fighting or bullying, and that in certain types of social animals, more socially dominant animals may monopolize certain valuable (to them) parts of the enclosure.

An example: aquatic turtles require exposed basking spaces. If there is not enough room for all of the turtles to bask at once, there will be competition over this valuable area, leaving some turtles without access to the appropriate amount of light. This is termed “cryptic overcrowding,” because it can occur in a tank which may, to all appearances, have more than adequate swimming space.

Cryptic overcrowding can be avoided by spreading out resources and preventing “bottleneck” areas where a single animal can blockade or corner others. But in general, the increase in space when adding more animals to an enclosure is not a linear equation. It will depend, again, on the behavior of the species.

Independent dividers like these can help reduce cryptic overcrowding in terms of agonistic behavior. Lower-ranking horses housed in group stalls spend more time lying down when they were out of sight of higher-ranking ones.

Movable dividers like these can help reduce cryptic overcrowding in terms of agonistic behavior. Lower-ranking horses housed in group stalls spent more time lying down when they were out of sight of higher-ranking ones. (Source: thehorse.com)

Aquatic or semiaquatic animals pose a unique challenge when it comes to space. Firstly, movement in water takes less energy than movement on land, so swimming animals need somewhat more space to perform activities with than you would expect for land animals. Secondly, a stable water condition is harder to maintain when there is less water in a system. Dissolved chemicals such as ammonia can be toxic to aquatic animals that breathe through gills or damage their skin, and being in containers with less water means that anything that gets into it will become more concentrated. So the smaller the system, the more dangerous any change in water quality will be.

Betta 'cubes' and vases have popped up on the market recently as viable ways to keep these solitary fish. While they can theoretically be kept in such a small space with adequate filtration and heating, the reality is that ammonia waste will build up so rapidly in such a small volume of water that the fish will be in constant stress and indeed life-threatening danger. Ironically, small and micro-aquariums are best left only to the most experienced aquarists.

Betta ‘cubes’ and vases have popped up on the market recently as viable ways to keep these solitary fish. While they can theoretically be kept in such a small space with adequate filtration and heating, the reality is that ammonia waste will build up so rapidly in such a small volume of water that the fish will be in constant stress and indeed life-threatening danger. Ironically, small and micro-aquariums are best left only to the most experienced aquarists.

Some aquariums and other places with large numbers of captive fish will mitigate this issue by keeping the fish in individual tanks connected to a larger flow-through system. In this case, even though the fish may be contained to one area, the amount of water it is living in is actually as large as the entire complex of tanks. In some cases, actual seawater may be cycled through the system via ocean pipes.

Aquatic research or cultivation facilities generally use flow-through water cycling.

Aquatic research or cultivation facilities generally use flow-through water cycling.

Speaking of complexes, there is a way to artificially enlarge an animal’s space: separation and barriers. An open field is not particularly difficult to navigate if one wants to go from one end to the other, but by adding a simple kind of maze, differing topography, or even just visual barriers, the time and energy it takes an animal to traverse the same distance will increase.

One excellent example of this is “Paddock Paradise,” a method of altering horse pastures so that the horses will be motivated to move constantly throughout the day. Ironically, it does this by reducing the total pasture space available by fencing off the center of the pasture so that it becomes a looping track.

Diagram of how to turn existing pasture into 'paddock paradise.' More elaborate designs include areas with wading pools, rocky terrain, etc.

Diagram of how to turn existing pasture into ‘paddock paradise.’ More elaborate designs include areas with wading pools, rocky terrain, etc.

This means that the horses will consume the available grass more quickly and be driven to move more often to seek patches to forage in. It also encourages herds to be kept in tighter groups rather than spread out across the pasture, which more closely mimics how they behave in the wild. Early studies suggest that horses kept in Paddock-Paradise style enclosures move about twice as much as those kept in traditional pastures- even though they often have far less available space.

In general, whether or not an animal has adequate space in its enclosure can be assessed by observing where it spends most of its time. “Overutilized” spots, i.e. places where the animal spends a disproportionate amount of time should be replicated or expanded, while places the animal barely or never uses could be eliminated (with the exception that they may provide space for infrequent but still vital behaviors like elimination). I encourage those of you reading along at home to think about the spaces your pet might over- or underutilize within the enclosure you have given it.

So, to sum it all up: while amount of available space is one of the most oft-cited concerns about captive animal welfare, simply adding more space to an enclosure is unlikely to improve an animal’s quality of life unless that space is specifically tailored to the animal’s activities. To this end, there is no hard and fast equation to help one to determine the amount of space an animal will need. Just as a human can be sufficiently entertained in a small apartment with a treadmill and access to the internet, it may be possible to humanely keep an animal in a relatively small space so long as the space is used wisely.

That’s it for part two- next, let’s discuss the importance of climate for captive animals.

(If you missed it, here’s part one of this series on captive animal enclosures!)

References and Further Reading

Carlstead, K., & Shepherdson, D. (2000). Alleviating stress in zoo animals with environmental enrichment. The biology of animal stress: Basic principles and implications for animal welfare, 337-354.

Clark, J. D., Baldwin, R. L., Bayne, K. A., Brown, M. J., Gebhart, G. F., Gonder, J. C., … & VandeBer, J. L. (1996). Guide for the care and use of laboratory animals. Washington, DC: Institute of Laboratory Animal Resources, National Research Council, 125.

Cornetto, T., & Estevez, I. (2001). Influence of vertical panels on use of space by domestic fowl. Applied Animal Behaviour Science, 71(2), 141-153.

Hunter, S. C., Gusset, M., Miller, L. J., & Somers, M. J. (2014). Space use as an indicator of enclosure appropriateness in African wild dogs (Lycaon pictus). Journal of applied animal welfare science: JAAWS, 17(2), 98.

Imfeld-Mueller, S., & Hillmann, E. (2012). Anticipation of a food ball increases short-term activity levels in growing pigs. Applied Animal Behaviour Science, 137(1), 23-29.

Jackson, J. (2006). Paddock Paradise: A Guide to Natural Horse Boarding. Star Ridge Publishing.

Leone, E. H., & Estevez, I. (2008). Use of space in the domestic fowl: separating the effects of enclosure size, group size and density. Animal Behaviour, 76(5), 1673-1682.

Mason, G. J. (2010). Species differences in responses to captivity: stress, welfare and the comparative method. Trends in Ecology & Evolution, 25(12), 713-721.

Morgan, K. N., & Tromborg, C. T. (2007). Sources of stress in captivity. Applied Animal Behaviour Science, 102(3), 262-302.

Reinhardt, V. I. K. T. O. R. (1992). Space utilization by captive rhesus macaques. Animal Technology, 43(1), 11-17.

Roberts, M., & Cunningham, B. (1986). Space and substrate use in captive western tarsiers, Tarsius bancanus. International journal of primatology, 7(2), 113-130.

Ross, S. R., Schapiro, S. J., Hau, J., & Lukas, K. E. (2009). Space use as an indicator of enclosure appropriateness: A novel measure of captive animal welfare. Applied Animal Behaviour Science, 121(1), 42-50.

Ross, S. R., & Lukas, K. E. (2006). Use of space in a non-naturalistic environment by chimpanzees (Pan troglodytes) and lowland gorillas (Gorilla gorilla gorilla). Applied Animal Behaviour Science, 96(1), 143-152.

Warwick, C., Arena, P., Lindley, S., Jessop, M., & Steedman, C. (2013). Assessing reptile welfare using behavioural criteria. In Practice, 35(3), 123-131.

Watters, J. V. (2014). Searching for behavioral indicators of welfare in zoos: Uncovering anticipatory behavior. Zoo biology, 33(4), 251-256.

Young, R. J. (2013). Environmental enrichment for captive animals. John Wiley & Sons.